Semibright nickel deposition



r a bright or mirror-likefinish were Patented Apr. 13, 1943 I UTE sA'I'ES -'r orries I 2.31am snmnmen'r NICKEL nsrnon Andrew Wesley,Plainfleld, N. 3., andliay Wil- ,liam Carey, Lynbrook, N. Y.,asslgnorsto The International Nickel Company, Ina, New York, N; Y., acorporation'of Delaware Application au ust 30, 1959, Serial No. 292,696

6 Claims: (011 204-49) appearance. =In order to avoid the expense anddisadvantages inherent in such prior art practice, many attempts havebeen made to produce nickel 1 coatings which were so smooth that no oronly slight bufilng was required trbring out a high luster. Coatingswhich gave a specular reflection without bufilng were known in the artas bright whereas those which had the appearanceof a mirrored surfacethat had been breathed upon and which required only slight bufilng toproduce designated semi-bright or blushed.", The art in recent years hasattempted to produce bright depositsby the use of .brightening additionagents" in the electroplating bath. These agents were, genreallyspeaking, additions of organic or inorganic materials such as sulionatednaphthalene or terpene compounds, albumins. cadmium salts and lead saltsintended to give bright or semi-bright deposition-were of the brightnickel type; In the event'that an ordinary nickel plating bath were usedit was customary to bufl the final nickel layer as well as theintermediate copper layer.

A serious difliculty accompanied the extensive buil'ing necessary tobring ordinary nickel platings to the bright'condition. As a resultpfthis extensive buillng the tendency to cut through the plate at thecorners and at raised portions "deposits directly in the bath. Even withthe most recent improvements, this art suflered fromseveral-disadvantages which limited the commercial usefulness of bathscontaining brightening addition agents. The chief disadvantage was thedifllculty of maintaining the bath composition constant over a period oftime. The brightening was appreciable. The semi-bright deposit of thepresent invention eliminates the necessity of extensive bufling and thuseliminates the danger of cutting through with its accompanying toll ofrejects j l v There was a definite and well recognized need in the artfora methodof depositing single layer coatings of'nickel free from pitsand smooth enough to buff-easily and which was not subject to theoperating difllculties mentioned hereinabove. However, when attemptshave been made to eliminate extensive buillng'and deposit nickeldirectlytcn iron, experts in the art advised against the use of a nickelchloride bath due to the poor 7 .bond formed between the coating andthecore plating peeling oifa metal which resulted in the short timeafter deposition.

We have invented a process of electrodepositing nickel free from pitsand in such sniooth form that a high luster can be developed by slightbumng. In our novel and improved process an easily controlledelectroplating solution composed substantially entirely of an aqueoussolution of addition agents were not perfectly stable; were vdiilicultto maintain in constant "concentration in the bath, and in part aredeposited on the ob- :Iect being plated. So much highly'skilledtechnical service had 'to be given to users of such baths that none ofthem was in widespread use in smaller plating shops. Other shortcomingsof these processes were extreme brittleness oi the deposit, a pronouncedtendency for development of pits in the deposit, and with some platingbaths 7 the permissible variation in plating conditions such astemperature and current density was very narrow with the result thatfrequently only part of-therplated article would be bright as plated sothat bufllng was required to develop a uniform bright finish.

Due to the difllculty of ionsmn'ciand' bunt-gt nickel chloride and boricacid in critical amounts is' used and the plating conditions includingthe hydrogen ion concentration temperature and current-density arecontrolled within critical limits properly correlated with the bathcompoordinary matte electrodeposited nickel coatings j and of gettingcoatings ofnickel rree'r m. pits, meta, having a-nrei'erred it wascommon practiceto'use multiple coatings of nickel and copper and toconfine the polishing sition to produce satisfactory and acceptablesemi-bright nickel deposits. 7 It is an object of the present inventionto provide semibright coatings of nickel which-may be brought to a highluster with only slight butt-r ing. a

' It is another object of the present invention to provide semi-brightdeposits of nickel having a preferred crystallographic orientation withthe 1 direction normal to the surface of the basis metal.

It 'is a further' obiect oi' the present invention.

to provides'emi-bright single layer coatlngs of nickel on othermetalssuch as iron, steel, brass,

. face and'a preponderance of crystals having their (I l I) face:developed in heavyldeposits.

,The invention also contemplates providing relatively thick,comparatively ductile coatings of electrodeposited nickel free from pitsand having a grain size greater than 0.0001 mm. and which are so smooththat they may be brought to a high luster with slight bufling.

Other objects and advantages of the present invention will becomeapparent from the following description taken in conjunction with theaccompanying drawings in which:

Fig. 1 is a graph showing the result of a physical test fordistinguishing between matte. semibright or bright deposits;

Fig.2 is a return reflection curve showing the intensity of reflectedlight at various angles from a heavy semi-bright nickel deposit; and

Figs. 3, 4 and 5 depict graphically the critical correlation betweentemperature and current density at pH values of 0.75, 1.0 and 2.0,respectively.

Generally speaking, the semi-bright nickel coatings of. the presentinvention may be obtained on any appropriate foundation metal or alloy.We prefer to use a plating bath containing principally nickel chlorideand boric acid in aqueous solution without "brightening additionagents," and by properly correlating hydrogen ion concentration, currentdensity and temperature within critical limits, as hereinafterdescribed. The present invention makes it possible to produce directlythick deposits of semi-bright nickel so smooth that they require onlyslight bufling to be brought to a high luster. At the same time thedeposits are satisfactory in respect to adherence, ductility, soundnessand freedom from pits. The semi-bright nickel deposits of the presentinvention may be obtained directly on iron or steel,

and the nickel plating so produced adheres well and has no tendency topeel off and is suitable for subsequent plating with chromium or othermetals.

In the preferred plating bath employed in the present chloride and boricacid are dissolved in water. Preferably the bath contains about 300grams per liter of nickel chloride and about 30 grams per liter'of boricacid. No addition of brightening agents of any kind need be made to thepresent improved bath to obtain the desired semi-bright nickel deposits.The boric acid content may vary from more than about 35 grams per literdown to less than about 5 grams per liter. Satisfactory results may beobtained provided more than a critical minimum content of boric acid ispresout. If boric acid is present in an amount less than 5 grams. thesemi-bright nickel deposit is burned and unsatisfactory. Beyond about 35grams of boric acid per liter, the solubility of boric acid at roomtemperature is exceeded and flakes of boric acid settle out when thebath is allowed to cool. About 35 grams of boric acid per literrepresents a practical maximum for commercial and industrial operationsbut the present invention is not limited to this amount as an absolutemaximum. Satisfactory results maystill be obtained when the boric acidconcentration is substantially equal to saturation at the operatingtemperature. While the theoretical function or functions of boric acidin its unique cooperation and combination with nickel chloride in thebath are not thoroughly understood. it is believed that boric acid doesserve to bufier the solution. Between the limits of about 260 grams andabout .340 grams "of NiClz.6H2O per liter satisfactory Y semi-brightdeposits are obtained. Either above invention, critical amounts ofnickel or below these critical limits. matte deposits are formed.

The acidity limits for producing satisfactory semi-bright depositshaving preferred crystallographic orientation with the nickelchloride-boric acid bath are within the limits of about pH=0.7 and aboutpH-=3.0 (electrometric). While satisfactory deposits are obtained frombaths operated within these limits, we prefer to maintain a pH of about1 when depositing semi-bright platings of nickel. The pH is maintainedby additions of hydrochloric acid instead of the customary sulfuricacid. These limits are critical. Numerous experiments have demonstratedthat satisfactory semi-bright deposits cannot be obtained with the abovementioned bath unless the pH value is less than 3.0. Below a pH of about0.7. the cathode current efllciency becomes too low for satisfactorycommercial operation.

Bath temperature and current density must be coordinated with each otherand with the hydrogen ion concentration in order to dbtain the desiredsemi-bright deposit of nickel. These relationships are depictedgraphically in Figs. 3, 4 and 5 in which the abscissa represents currentdensity in amperes per square foot, and the ordinate is temperature indegrees Fahrenheit. The bath employed for each series of tests containedabout 300 grams per liter of NiClaGHaO and about 30 grams per liter ofboric acid with the pH and other plating conditions controlledashereinafter set forth.

In'one series of tests, a constant pH of about 0.75 was maintainedwhile'current density and bath temperature were varied. Currentdensities from very low values to more than 200 amperes per square footwere found to produce satisfactory semi-bright nickel deposits providedthe bath temperature did not rise above a critical value indicated bythe curve D in Fig. 3.

' Below the curve D satisfactory semi-bright deposits were obtained, butabove the curve the deposits were matte. 1

The pH value was maintained at about 1.0 for a second series of tests inwhich both temperature and current density were varied. .Within the areadefined by curves E and F in Fig. 4

' satisfactory semi-bright deposits were produced.

When the temperature lay above curve E at any particular current densitythe deposit was matte. Below curve F, the deposit is burned andunsatisfactory.

In Fig. 5, the results series of tests conducted at a pH of about 2.0.

The area between the curves G and H represents the conditions oftemperature and current density which yield satisfactory semi-brightnickel deposits. Above curve G and below curve H the deposits are matteand burned respectively as described in connection with .Fig. 3.

It will be seen from a study of Figs. 3, 4 and 5 that the area definingthe ranges of permissible temperatures and current densities decreasesprogressively as the pH rises. A fourth series of tests conducted atpH=3.0 demonstrated that the semi-bright area had substantiallydisappeared. While the operable range of pH is about 0.7 to about 3.0,practical limits for semi-bright plating on a commercial scale are aboutpH=0.75 and about pH=-2.0. Temperatures from about F. to about F. aresatisfactory for commercial operation with current densities varyingfrom about 20 to about 200 amperes per square foot. Current density,temperature and pH should preferably be so correlated as to fall wellare plotted of a third 2,816,803 .within the semi-brightareas of ll'igs.s,- 4 and 5. A

It will be understood by those skilledin the art that lines of curves D,E, F, G andH actually represent areas of somewhat varying width.

' .In other words, for any given current density and pH, e. g., 140amperes'per square foot and .pH= 1, the deposit does not suddenly change.from semi-bright to' mattewith a slight tempera-' ,ture change, e. g.,from slightly less to slightly morethan 141525. (see Fig. 4). On thecontrary, there is a relatively narrow temperature range over which thedeposit changes rather rapidly from semi-bright to matte.

The following specific example is illustrative of the results that canbe obtained by practicing I the present invention. An aqueous platingbath was prepared having the following composition:

'mchcmo about 300 grams per liter I HaBOa about 30 grams per literSufllcien't hydrochloric acid was added to the aqueous solution toadjust the pH to about 1.0.

A bagged, rolled, depolarized nickel anode was used and the solution wasfiltered continuously.

Slight'agitation of the bath was obtained by means of a gentle streamoi? air. The bath temperature was maintained at about 110 F. while asteel object was coated directly 'with nickel at a cathode currentdensity of about 75 amperes per square foot. After about '19 minutes asemibright deposit about 0.001 inch thick had been formedwhichwastbrought to a high finish in a was illuminated by a narrow collimatedbeam of single bufling operation using a soft rag wheel treated with anordinary 'grease coloring compound containing rouge. A bright,mirror-like surface was obtained at a given point in about 10 seconds.

white light of about 1500 foot candlesintensity,- incident upon thespecimen at various known angles with respect to the surface of thespecimen.

The intensity of the light reflected directly back from the specimenparallel tothe impinging beam of light was measured by an illuminometer.By

incident beam, data for curves correlating the angle of incidence (whichin'this procedure is the same as the angle of reflection) and theintensity of the light reflected back along the path of the illuminatingbeam were obtained.

These data for typical matte, semi-bright and' bri ht specimens withcoatings 0.001 inch thick are plotted in curves 1, J and K of Figure 1which indicate quite different magnitudes and distribu-- more maxima inthe curve with a maximum ob-- served intensity within the range of about30 to about 600 foot candls when the incident light has an intensity ofabout 1500 foot candles, i. e.,

the maximum intensity of reflected light is about 2% to 40% of theincident light. Typical matte deposits, however. reflect light of lessthan 20 foot candles intensity under comparable conditions over a widerange of angles of incidence and reflection, i. e., about 1.5% or less.

Blight bumng of the semi-bright deposit, for

and in a plane normal to the table. The sample inclining the specimen atvarious angles to the .10

example, with a rag bufling wheel and ordinary The art recognizes threegeneral classesof A nickel plating, viz., the ordinary white nickel,

bright nickel and semi-bright or blushed nickel. The term white" nickelhas been used to describe the color of matte deposits and has noreference to any degree of brightness. A bright deposit is one wh chgives a specular reflection of incident light and is mirror-like inappearance. Im-

, ages 01 objects seen in aflat surface coated with bright nickel appearclear and distinct. A dull or matte deposit is one whichrefiects solittle light specularly that no images can be distinguished in a flatsurface coated with matte nickel except at grazing angles of incidence.Instead of specular, there is diiiusereflection. A.semibright deposit isone approaching the smoothness of a bright deposit but falling somewhatshort of light is reflected specularly that images of objects can bedistinguished at fairly small angles of incidence, albeit not veryclearly and with hazy, instead of sharp, edges.

In order to define more precisely the (inference between matte.semi-bright and bright deposits,

"return reflection measurements were made by the method originated by P.Bouger [Traite d'Qp. 'tique sur la Gradation de la Lumiere, Paris.

, Guerin and Delatour (1760),]. In obtaining these data, the specimen,-in the form ofaplanerec-.

' tang'ular piece of steel sheet coated with a nickel deposit about0.001 inch thick, was placed at the -.center of a spectrometertablewhich permitted the angle of the test sample with respect to the rougebumng compound for about 10 seconds, produced a bright, mirror-likefinish at any particu{ lar spot. Deposits as thick as about 0.006 inchmay be obtained readily by the process embodying our invention which arestill semi-bright and readily polished with slight bufilng to bright,

T mitror-like finish.

niflcance of various typesof such curves. That.

In'evaluating the significance of the 'curve 01" Fig. 2 it is necessaryto consider briefly the sigof a perfect reflector would have its maximumin-' a specular reflection of incident light. It appears I like a mirrorthat has Just'been lightly breathed on. The terms "blushed" and "milkyare also used to describe semi-bright deposits. Enough v impinging lightbeam to be altered and measured tensity at 0 to the normal to the planereflection and zero intensity for all other inclinations of thespecimen. This would indicate that the faces ofall the smallcrystallites. were parallel to the specimen surface or'that the surfacehad been flowed into a plane as in polishing or that the crystalliteswere smaller than the wave length of the incident light. As the anglesof the reflecting facets increased, this curve would broaden out, thepeak intensity decreasing. This could continue until the limiting.casewas reached, assuming, naturally, that the angular distribution ofrefleeting facets was perfectly haphazard, for which the intensity wasconstant for any angle of inci- 4 dence and reflection, i. e., eachordinate was the same, and the curve becamevery flat topped. If for anyreason the facets tended to assume a par- 1 tic'ular angle we shouldexpect to find a peak at this particular angle 01 incidence.

The general shape of all reflectivity'vs. angle I curves will vary inthe manner indicated-above,

then, depending solely upon the angle that the facets of, the individualcrystals make with the mean "plane" surface. An infinite number ofvariations'could be secured-however, by increasing the roughness of thesurface. As this was done, two thingswould take place: mat, theefl'ective illumination of the surface would be decreased because onlythe hills would be lighted at most angles of incidence; and second, theincident light would be multiply reflected with some loss at eachreflection, i. e., the hills" could block off the reflected light aswell as the incident light and the surface would be considered dark. Inaddition to these obvious effects, it is possible toget a certain amountof extinction by interference.

The greater the amount of light absorbed. nattical reflectioncharacteristics,'X-ray studies were made to determine the nature of theorientation of the crystals comprising the several types of deposits.These showed that the dark matte deposit had a random orientation andthat thesemibright deposit had a strongly preferred orientation with the[II2] direction normal tothe plane of the specimen. Previous work hadindicated that, with nickel, the (III) planes were developed in theplating process. With these planes developed in deposits having the l' II2] direction normal to the plane ofthe sample, maxima in the opticalreturn reflection would be expected at 19 2 to the normal which checksclosely with the observations on the 0.0036 inch deposit discussedearlier. Thin deposits did not show two maxima in the oopticalreflection studies, but this may have been due to the lack of perfectionin the (III) planes at this stage of the plating operation;

As stated above X-ray studies showed that the [I I2] direction ofsemi-bright deposits was normal to the plane of the specimen which meansthat the I I2) planes are parallel to the plane of the specimen; sincethe (III) facesmake only a small angle (i..e. 19 /2") with the (H2)planes, it is to be expectedthat the surface of the semibrightelectrodeposit is microscopically almost flat,

which accounts for the fact that only a slight amount of buffing isrequired to develop the degree of flatness required for a truly brightfinish.

Departures from the plating conditions necessary for the production ofthe desired semi-bright plate with its highly preferred orientationcaused a decrease in the percentage of crystals oriented with the [H21normal to the plane of the specimen and the production of [H] and [I00]orientations, while still further departures in plating conditions causethe disappearance of the desired [H2] orientation and finally to asensibly random orientation. This behavior causes incontaining 0.9 molarnickel. chloride, 0.1 molar" nickel sulfate and 0.6 molar boric acid.The plating conditions were pH 3.0,\current density 0.5 amp. per sq.drn. and room temperature. Bozorth says nothing in his articleconcerning the appearance of the deposit. It was made upon a small Typoof preferred orientation (dirvction normal to base) Sourci-OperatorA...,. Operator B.

Operator Operator!) Random.

Do. I)". Do.

It seems probable that the bright nickel deposits of commerce are brightprimarily because their grain size is less than that of the wave lengthof visible light.

when metallographically prepared sections are examined, hence theirgrain sizes are greater than that of the wave length of visible light.

The existence of a high degree of preferred orientation with the II IZIdirection normal to the plane of the sample is a unique distinguishingcharacteristic of the semi-bright deposits of the present invention. Thedark matte deposists from" the same chloride bath all showed randomorientation. The light matte deposits from the same bath show thepresenceof several types of preferred orientations at the same time; amixture of [I00], lIIO] and [H2] when made under border-line conditions,and [I00] and [I I0] if the deposits were formed under conditions quiteremote from the critical conditions for semi-bright deposits.

To demonstrate in a-quantitatlve manner the importance of the presentinvention in producing an easily polished plate, determinations weremade of the amount of nickel removed in buliing nickel plates of thesame initialthickness on both sides.

It should be emphasized that both the matte and semi-bright plates whosepolishing characteristics differed so markedly were produced in the samebath-one operated outside the semibright range and one within it.

The present application is a division in part and a continuation in partof our copending United States application Serial No. 248,146 filedDecember 29, 1938.

Although the present invention has been de- The semi-bright depositsv ofthe present invention show a definite structure scribed in combinationwith certain preferred embodiments thereof, it is to be understood thatmodifications and variations may be made as those skilled in .theartwill-readily understand.

It is to be understood that such variations and modifications are to beconsidered within the purview of the specification and the scope of theappended claims.

We claim:

1. As a new article of manufacture, a composit article comprising ametallic core'and an electrodeposited protective nickelous layer atleast 0.0001 inch thick having a semi-bright finish containing grains ofa size greater than 0.0001 millimeter, said grains having preferredcrystallographic orientation with the [H2] direction substantiallynormal to the surface of the core.

1 [H21 direction practically normal to the surface 2. As a new articleof manufacture, a com- I posite article comprising a metallic core and athick electrodeposited nickelous protective layer,

said nickelous protective layer being about 0.0036 inch to about 0.006inch thick, containing grains of a size greater than 0.0001 millimeter,having preferred crystallographic orientation with the [I I2] directionsubstantially normal to the surface of said core and havingtwo maxima oflight reflectively at about 20 to the normal of said layer. I

3. As a new article ofmanufacture, a composite article comprisinga-metallic core and a thin electrodeposited nickelous protective layer,

said nickelous protective layer being at least 0.0001'inch and less than0.0036 inch thick, having one maximum of light reflectivity, having apreferred crystallographic orientation with the plane of said articleand having a grain size greater than about 0.0001 millimeter.

4. As a new article of manufacture, a composite article having a ferrouscore and a directly electroplated firmly adherent electrodepos'itedlayer substantially of nickel, said layer of nickel being at least0.0001 inch thick, containing grains of a size greater than 0.0001millimeter, having a semi-bright finish and having a preferredcrystallographic orientation with the [I I2] direction practicallynormal to the surface of said article.

5. As a newarticle of manufacture, a composite article consisting of aferrous core and anelectrodeposited outer layer, said outer layer beingI about 0.0036 inch to about 0.006 inch thick comprising substantiallyelectrodeposited nickel having a grain. size greater than the wavelength of visible light and said electrodeposited nickel havaunnizwWESLEY.

JAY WILLIAM CAREY.

